Ophthalmic composition comprising a prostaglandin

ABSTRACT

The present invention relates to a pharmaceutical composition suitable for ophthalmic use comprising one or more prostaglandin derivatives or salts, a stabilizing amount of polyethylene glycol hydroxystearate and pharmaceutically acceptable vehicle.

FIELD OF THE INVENTION

The present invention relates to pharmaceutical composition suitable forophthalmic use comprising prostaglandin derivatives.

BACKGROUND OF THE INVENTION

Prostaglandin derivatives are one of the known poorly soluble drugs andare administered via ophthalmic route for treating elevated intraocularpressure. One of the prostaglandin derivatives, latanoprost has beenapproved in the United States of America for the reduction of elevatedintraocular pressure in patients with open-angle glaucoma or ocularhypertension, and is commercially available in the United States ofAmerica, under the brand name of XALATAN®. XALATAN® Sterile OphthalmicSolution is a clear, isotonic, sterile, buffered aqueous solution oflatanoprost 0.005% (50 μg/ml) with 0.02% benzalkonium chloride and otherexcipients, and having a pH of approximately 6.7 and an osmolarity ofapproximately 267 mOsmol/Kg. It is supplied in clear low densitypolyethylene bottle with a clear low-density polyethylene dropper tip, aturqouise high density polyethylene screw cap and a tamper-evident clearlow-density polyethylene overcap. It is recommended for this productthat the unopened bottles be stored under refrigeration at a temperatureof approximately 2-8° C. and during shipment to the patient, the bottlemay be maintained at temperature up to 40° C. for a period not exceeding8 days. Once the bottle is opened for use, it may be stored at roomtemperature up to 25° C. for 6 weeks.

Another prostaglandin derivative, which has been approved in the UnitedStates of America for the reduction of intraocular pressure in patientswith open-angle glaucoma or ocular hypertension is unoprostoneisopropyl. It is commercially available under the brand name ofRESCULA®. RESCULA® is a sterile, isotonic, buffered aqueous solution ofunoprostone isopropyl 0.15%, with 0.015% benzalkonium chloride and otherexcipients and having a pH of approximately 5.0-6.5 and an osmolality of235-300 mOsmol/kg. It is supplied in clear, natural polypropylene bottlewith a natural polypropylene dropper tip, a turquoise polypropyleneclosure and a clear tamper-evident shrink band. The recommended storagetemperature for the product is between 2° C. to 25° C.

A pharmaceutical composition suitable for ophthalmic use is generallyfilled in small volume containers made up of plastics such aspolypropylene and polyethylene rather than rigid materials like glass.Glass is not suitable for making containers for ophthalmic use becauseit is generally not able to meet requirement of dispensing ophthalmicpreparations in very small volumes, for example drops.

The prostaglandin derivatives are known to be unstable either because ofabsorption or adsorption or degradation, when stored in polyethylenecontainers. For example, United States patent U.S. Pat. No. 6,235,781(herein after referred to as '781) shows that when the aqueouscomposition of prostaglandin is stored in polyethylene containers,percentage drug remaining was about 80% indicating loss of theprostaglandin derivatives. The '781 patent discloses a method ofincreasing the stability of an aqueous prostaglandin compositioncomprising a prostaglandin and a pharmaceutically acceptable surfactantwherein the method comprises: packaging the aqueous prostaglandincomposition in a polypropylene container, provided that thepolypropylene container is not packaged in a bag containing an ironoxide oxygen scavenger.

Another prior art, U.S. patent application No. 20050287325 (hereinafterreferred to as '325) discloses that latanoprost is prone to sorptiononto the naturally derived plastic containers. The '325 patentapplication claims a container comprising prostaglandin compositionsthat exhibit less than 20% sorption of the prostaglandin. The containersare restricted to those made of specific polyolefins, such as DuPont® 20LDPE, Chevron 5502 HDPE, Atofina 3020 PP, polypropylene homopolymers,low ethylene content (<8%) polypropylenes, and polymers (HDPE, PP) withlow content of additives (<5%) and with low flexural modulus (<200kpsi).

U.S. patent application US20060100288 (herein after referred to as '288)discloses an oil in water type emulsion, which comprises colloidparticles having an oily core surrounded by an interfacial film, whereinsaid interfacial film has an overall positive charge and comprises:

-   -   1) 0.001% to 0.1% by weight of a cationic agent,    -   2) 0 to 1% by weight of a non ionic surfactant, and    -   3) 0 to 0.5% by weight of an anionic surfactant,        with at least one of said ionic surfactant and of said anionic        surfactant being present. The patent application discloses the        use of polyethylene glycol hydroxystearate as one of the        non-ionic surfactant that should be used in combination with a        cationic agent.

In an attempt to develop a pharmaceutical composition of prostaglandinor its derivatives which can be effectively stored in naturalpolyethylene containers without any drug loss, the inventorssurprisingly found that when the prostaglandin derivatives wereformulated with polyethylene glycol hydroxystearate, the sorptionproblem was reduced substantially. When small amount of oil was added tothis pharmaceutical composition, the sorption of prostaglandinderivatives to the polyethylene containers was further reduced. It wasalso found that an addition of a very small amount of oil gave apharmaceutical composition comprising prostaglandin and polyethyleneglycol hydroxystearate that is non irritant to the ocular mucosa, withimprovement in the sorption problem, i.e, no sorption of prostaglandinderivatives onto the low density polyethylene containers.

OBJECTS OF THE INVENTION

It is an object of the present invention to make clear pharmaceuticalcompositions suitable for ophthalmic use and containing poorly watersoluble drugs like prostaglandin derivatives, for example, latanoprost.It is another object of the present invention to make a stablepharmaceutical composition comprising prostaglandin derivatives.

It is yet another object of the present invention to make apharmaceutical composition suitable for ophthalmic use comprisinglatanoprost that shows no sorption to the low density polyethylenecontainers (LDPE).

It was another object of the invention to make a pharmaceuticalcomposition suitable for ophthalmic use comprising prostaglandinderivatives free of quaternary ammonium derivatives.

It is yet another object of the present invention to make apharmaceutical composition suitable for ophthalmic use comprisingprostaglandin derivatives by using a process that is economical in termof energy and time consumption and is further suitable for large scaleup.

It is further object of the invention to provide a pharmaceuticalcomposition suitable for ophthalmic use comprising prostaglandinderivatives that causes no irritation to the ocular mucosa.

It is further object of the invention to provide a pharmaceuticalcomposition suitable for ophthalmic use comprising prostaglandinderivatives that is effective in lowering the intraocular pressure.

It is further object of the invention to provide a pharmaceuticalcomposition suitable for ophthalmic use comprising prostaglandinderivatives wherein the composition upon administration shows reducedocular pigmentation.

It is further object of the invention to provide a pharmaceuticalcomposition suitable for ophthalmic use comprising prostaglandinderivatives that is stable on storage at room temperature.

It is also the object of the present invention to provide a clearpharmaceutical composition suitable for ophthalmic use, said compositioncomprising prostaglandin derivatives.

SUMMARY OF THE INVENTION

The present invention provides a pharmaceutical composition suitable forophthalmic use, said composition comprising

-   -   a) prostaglandin derivatives or pharmaceutically acceptable        salts    -   b) stabilizing amount of polyethylene glycol hydroxystearate        and a pharmaceutically acceptable vehicle.

The present invention also provides a pharmaceutical compositionsuitable for ophthalmic use, said composition comprising

-   -   a) prostaglandin derivatives or pharmaceutically acceptable        salts    -   b) stabilizing amount of polyethylene glycol hydroxystearate    -   c) oil        and a pharmaceutically acceptable vehicle.

DETAILED DESCRIPTION OF THE INVENTION

The term ‘emulsion’ is used to mean a homogenous mixture of two liquidphases which do not normally mix such as oil and water. An ‘emulsifier’is a substance which aids the formation of an emulsion. The terms‘emulsifier’ and ‘surfactant’ are used interchangeably herein.

The term ‘microemulsion’ as used herein means a thermodynamically stabledispersion of two immiscible liquids, stabilized by surfactants; it istypically clear because the dispersed droplets are less than 100nanometers in diameter.

The term ‘self emulsifying’ means an emulsion that is formedspontaneously without any external energy supply.

The term ‘Percent Transmission’ as used herein is defined as follows.When light is allowed to pass through a solution, the percentage ofincident light which is transmitted through the solution is referred toas “Percent Transmission”. The “percent transmission” generally definesthe visible clarity of the composition.

According to one embodiment, the present invention provides apharmaceutical composition suitable for ophthalmic use, said compositioncomprising

-   -   a) prostaglandin derivatives or its pharmaceutically acceptable        salts;    -   b) stabilizing amount of polyethylene glycol hydroxystearate        and a pharmaceutically acceptable vehicle.

According to one embodiment, the present invention provides apharmaceutical composition suitable for ophthalmic use, said compositioncomprising

-   -   a) prostaglandin derivatives or its pharmaceutically acceptable        salts;    -   b) stabilizing amount of polyethylene glycol hydroxystearate    -   c) oil;        and a pharmaceutically acceptable vehicle.

According to one embodiment of the present invention, there is provideda pharmaceutical composition suitable for ophthalmic use, saidcomposition comprising

-   -   a) latanoprost or its pharmaceutically acceptable salts    -   b) stabilizing amount of polyethylene glycol hydroxystearate    -   c) castor oil;        and a pharmaceutically acceptable vehicle.

According to one embodiment of the present invention, there is provideda pharmaceutical composition suitable for ophthalmic use, saidcomposition comprising

-   -   a) travoprost or its pharmaceutically acceptable salts    -   b) stabilizing amount of polyethylene glycol hydroxystearate    -   c) castor oil;        and a pharmaceutically acceptable vehicle.

According to one embodiment of the present invention, there is provideda pharmaceutical composition suitable for ophthalmic use, saidcomposition comprising

-   -   a) bimatoprost or its pharmaceutically acceptable salts    -   b) stabilizing amount of polyethylene glycol hydroxystearate    -   c) castor oil;        and a pharmaceutically acceptable vehicle.

The prostaglandins derivatives that may be used in the pharmaceuticalcomposition of the present invention includes, but are not limited to,all pharmaceutically acceptable prostaglandins, their derivatives andanalogs, and their pharmaceutically acceptable esters and salts(hereinafter collectively referred to as “prostaglandins” or “PG's”),which are useful for reducing intraocular pressure when appliedtopically to the eye. Such prostaglandins include the natural compounds,such as for example PGE ₁, PGE ₂, PGE ₃, PGD₂, PGF_(1a), PGF_(2a),PGF_(3a), PGI₂(prostacyclin), as well as analogs and derivatives ofthese compounds which are known to have similar biological activities ofeither greater or lesser potencies. Analogs of the naturalprostaglandins include but are not limited to: alkyl substitutions(e.g., 15-methyl or 16,16-dimethyl), which confer enhanced or sustainedpotency by reducing biological metabolism or alter selectivity ofaction; saturation (e.g. 13,14-dihydro) or unsaturation (e.g.,2,3-didehydro, 13,14-didehydro), which confer sustained potency byreducing biological metabolism or alter selectivity of action; deletionsor replacements (e.g. 11-deoxy, 9-deoxo-9-methylene), which enhancechemical stability and/or selectivity of action; and omega chainmodifications (e.g., 18,19,20-trinor-17-phenyl, or17,18,19,20-tetranor-16-phenoxy), which enhance selectivity of actionand reduced biological metabolism. Derivatives of these prostaglandinsthat may be formulated in the compositions of the present inventioninclude all pharmaceutically acceptable salts and esters, which may beattached to the 1-carboxyl group or any of the hydroxyl groups of theprostaglandin by use of the corresponding alcohol or organic acidreagent, as appropriate. The terms “analogs” and “derivatives” includecompounds which exhibit functional and physical responses similar tothose of prostaglandins per se. Prostaglandins are well known in theart. Particular prostaglandins that may be formulated in thecompositions of the present invention include for example trimoprostil,rioprostil, cloprostenol, fluprostenol, luprostiol, etiproston,tiaprost, latanoprost, travoprost, bimatoprost, unoprostone and itsderivatives like unoprostone isopropyl, misoprostol, sulfoprostone,gemeprost, alfaprostol, delprostenate, and the like. Pharmaceuticalcompositions of the present invention include one or more prostaglandinsas described above in an amount between about 0.00001% w/v and about0.2% w/v.

In one embodiment of the present invention, latanoprost which is aprostaglandin F2a analogue, namelyisopropyl-(Z)-7[(1R,2R,3R,5S)3,5-dihydroxy-2-[(3R)-3-hydroxy-5-phenylpentyl]cyclopentyl]-5-heptenoateis used. It may be present in an amount ranging from about 0.00001% w/vto about 0.2% w/v. Preferably, latanoprost is used in amounts of about0.005% w/v. In another embodiment, travoprost is used as theprostaglandin derivative in amounts ranging from about 0.00001% w/v toabout 0.2% w/v preferably in an amount 0.004% w/v. In yet anotherembodiment, bimatoprost is used as the prostaglandin derivative inamounts ranging from about 0.00001% w/v to about 0.2% w/v, preferably inan amount 0.03% w/v.

Polyethylene glycol hydroxystearate is a non ionic surfactant having aHLB value in the range of 14.0 to 16.0. The surfactant has polyglycolester of 12-hydroxystearic acid (70%) as the hydrophobic component andpolyethylene glycol (30%) as the hydrophilic component. The main fattyacid component is 12 -hydroxystearic acid (12 HSA) with stearic acid andpalmitic acid also present in detectable amounts. SOLUTOL® HS 15 is onesuch polyethylene glycol hydroxystearate manufactured by BASF which iscommercially available as a white paste at room temperature.

The term ‘stabilizing amount’ as used herein means an amount ofpolyethylene glycol hydroxystearate that substantially reduces orprevents the adsorption of prostaglandin derivatives onto the containerswhen stored in containers such as those made up of low densitypolyethylene, during shelf-life of the product. The term ‘substantiallyreduces the sorption’ as used herein means that not more than 20% ofsorption of prostaglandin to the container; preferably not more than 15%of sorption of prostaglandin to the container, when the composition isstored at recommended temperature during the shelf life of the product.The said stabilizing amount of polyethylene glycol hydroxystearate isfound to cause no toxic effect or irritation to the ocular mucosa uponadministration for a long time.

The stabilizing amount of polyethylene glycol hydroxystearate accordingto the present invention ranges from about 0.001% to about 3.0% weightby volume of the composition. In the preferred embodiments of thepresent invention, the amount of polyethylene glycol hydroxystearate mayrange from about 0.1% to about 1.0%, preferably 0.2% to about 0.75%weight by volume of the composition. Further incorporation of oil in thecomposition allows a lesser stabilizing amount of polyethylene glycolhydroxystearate. For example, generally, when castor oil is added to thecomposition, the ratio of oil to polyethylene glycol hydroxystearate maybe less than 1.0.

According to one embodiment of the present invention, oil may be used incompositions. The oil used may be any oil derived from vegetable, animalor mineral source and/or mixtures thereof. Examples of oils that may beused in the pharmaceutical composition of the present invention,include, but are not limited to, castor oil, olive oil, peanut oil,sesame oil and the like and mixtures thereof. Preferably, thecompositions of the present invention comprise a vegetable oil such ascastor oil. The oil may be used in an amount ranging from about 0.005%w/v to about 1.0% w/v. Preferably, the oil is used in an amount rangingfrom about 0.05% w/v to about 0.5% w/v, most preferably the oil is usedin amounts ranging from about 0.1% w/v to about 0.3% w/v. In embodimentswhere the pharmaceutical composition is a self emulsifying composition,the amount of oil is critical. The amount of oil that may be used insuch compositions ranges from 0.1% w/v to 0.3% w/v.

The pharmaceutical composition may additionally comprise othersurfactants along with polyethylene glycol hydroxystearate. The term‘emulsifier’ and the term ‘surfactant’ may be used interchangeably.Examples of surfactants that have HLB value more than 10 is used in thepharmaceutical composition. The compositions of the present inventionalso comprises a surfactant/emulsifier or a mixture of emulsifiersselected from various emulsifiers as described inter alia in standardreference books like “Lachman's—The Theory and Practice of IndustrialPharmacy” 3^(rd) edition, pg-513-520, “Remington's PharmaceuticalSciences”, 18^(th) edition, pg 298-309, “Handbook of PharmaceuticalExcipients”, 3^(rd) Edition, pg-see index pg 652 entitled emulsifyingagents. The compositions of the present invention may use emulsifier(s)selected from the group consisting of non-ionic, cationic and anionicemulsifier. The emulsifier selected for the invention may be used in anamount ranging from about 0.001% w/v to about 2.0% w/v. Preferably, theemulsifier should be used in an amount ranging from about 0.01% w/v toabout 1.0% w/v. More preferably, the emulsifier should be used in anamount ranging from about 0.1% w/v to about 0.5% w/v. Preferably, thecompositions of the present invention use emulsifier(s) selected frompolysorbates, macrogols, poloxamers, tyloxapol, polyethylene glycolderivatives, polyvinyl alcohol and the like and/or mixtures thereof.

The compositions of the present invention comprises a pharmaceuticallyacceptable vehicle comprising excipients such as preservatives, osmoticagents/tonicity adjusting agents, buffering agents, pH adjusting agents,viscosity enhancers and other agents that may be used in formulating anophthalmic composition.

The pharmaceutically acceptable vehicle used in the compositionaccording to the present invention may comprise antimicrobiallyeffective amount of preservative or the composition may be selfpreserving.

In one embodiment of the present invention, the pharmaceuticalcomposition of the present invention contains preservatives inantimicrobially effective amounts. Antimicrobial effective amounts of apreservative may be determined by performing preservative efficacy testsor antimicrobial effectiveness tests. These tests are inter aliadescribed in chapter 51 of the United States Pharmacopoeia 29-NationalFormulary 24 (USP 29-NF 24). The preservatives may be used in an amountwithin the concentration ranges described in standard reference bookslike ‘Remington's Pharmaceutical Sciences’ and ‘Handbook ofPharmaceutical Excipients’.

The preservative may be selected from the group consisting of acids andtheir pharmaceutically acceptable salts such as sorbic acid, potassiumsorbate, boric acid, borax, salicylic acid, benzoic acid, lactic acid,acetic acid; Aldehydes such as thimerosal; Alcohols such as benzylalcohol; phenyl ethanol; Phenylmercuric salts such as phenylmercuricacetate and nitrate; Parabens such as methyl and propyl paraben; ethylparaoxybenzoate or butyl paraoxybenzoate; Halogenated alcohols such aschlorobutanol and the like, and combinations thereof.

Preferably, the compositions of the present invention comprise anantimicrobially effective amount of a preservative comprising a mixtureof at least two acid preservatives selected from the group consisting ofboric acid, benzoic acid, salicylic acid, sorbic acid, lactic acid andacetic acid or a pharmaceutically acceptable salt thereof. Morepreferably the pharmaceutical compositions of the present inventioncomprise a mixture of sorbic acid and/or its pharmaceutically acceptablesalt and boric acid and/or its pharmaceutically acceptable salt. Thesepreservatives do not present any irritating effects and have goodanti-microbial/anti-septic properties.

The term “sorbic acid” as used herein, applies to both sorbic acid andsorbate salts. Thus, sodium sorbate, potassium sorbate, ammoniumsorbate, or any salt of sorbic acid could be used in the methods andcompositions disclosed herein and should be interpreted to mean “sorbicacid”. It is understood that in an aqueous solution having a pH of 7,sorbic acid, which has a plc of 4.76 will be essentially completelydeprotonated. Thus, the actual form of sorbic acid in a composition maybe different than that which was added to the composition, and the term“sorbic acid” should be applied as broadly as generally understood inthe art in light of these considerations. The sorbic acid or its saltmay be used in amounts ranging from about 0.04% w/v to about 2.7% w/v.It is preferred that the sorbic acid or its salt be used in amountsranging from about 0.07% w/v to about 1.4% w/v. In a preferredembodiment, the preservative used is potassium sorbate in an amount ofabout 0.47% w/v or sorbic acid in an amount of about 0.35% w/v or about0.2% w/v.

The term “boric acid” generally refers to boracic acid and includesorthoboric acid and/or metaboric acid and/or tetraboric acid. Salts ofboric acid may typically include sodium borate, potassium borate,calcium borate, magnesium borate, manganese borate, and other suchborate salts. A preferred salt of boric acid used in the composition ofthe invention is sodium borate or borax, as it is commonly called. Theboric acid or its salt may be used in amounts ranging from about 0.001%w/v to about 4% w/v. It is preferred that the boric acid or its salt beused in amounts ranging from about 0.05% w/v to about 2% w/v. Inpreferred embodiments of the invention, the boric acid is used alongwith a pharmaceutically acceptable salt of boric acid. In a preferredembodiment of the invention, the boric acid and the borax are used inamounts ranging from about 0.05% w/v to about 2% w/v each. In aparticularly preferred embodiment, the boric acid and the borax are usedin amounts of about 0.1% w/v and about 0.11% w/v respectively. Inanother preferred embodiment, the boric acid and the borax are used inamounts of about 0.3% w/v and about 0.11% w/v respectively. The boricacid and borax mixture in addition to its antimicrobial or preservativeproperties also functions as a buffer in the composition and is commonlyreferred to as borate-boric acid buffer. The term “borate-boric acidbuffer” generally refers to any combination of boric acid and one ormore of the conjugate bases such that the pH is adjusted to the desiredrange, but preferably it refers to a combination of boric acid andborax. The preservatives that may be used in amounts ranging from about0.001% w/v to about 4% w/v. It is preferred that the two preservativesbe used in amounts ranging from about 0.01% w/v to about 2% w/v.

In addition to the mixture of at least two acid preservatives, thecomposition of the present invention may optionally contain a chelatingagent selected from the group consisting of ethylenediaminetetraaceticacid (EDTA); ethyleneglycol-bis-(b-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA);1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA);ethylene-N,N′-diglycine (EDDA); 2,2′-(ethylendiimino)-dibutyric acid(EDBA); and pharmaceutically acceptable salts thereof.Ethylenediaminetetraacetic acid (EDTA) or its salt, disodium edetate arepreferred as chelating agents which may be additionally added to thepreservative of the composition of the invention.Ethylenediaminetetraacetic acid (EDTA) or its salt such as disodiumedetate may be used in amounts ranging from about 0.009% w/v to about10% w/v. It is preferred that the EDTA or its salt be used in amountsranging from about 0.09% w/v to about 2% w/v. In a preferred embodiment,disodium edetate is used as the chelating agent in amounts of about 0.3%w/v of disodium edetate or 0.26% w/v of the EDTA.

The pharmaceutically acceptable vehicle may comprise of osmotic agents.Examples of the osmotic agents that may be used in the compositions ofthe present invention are selected from the group comprising sodiumchloride, potassium chloride, calcium chloride, sodium bicarbonate,sodium carbonate, magnesium sulfate, sodium hydrogen phosphate, sodiumdihydrogen phosphate, dipotassium hydrogen phosphate, mannitol, sucrose,glucose and the like, and mixtures thereof. It is known that to beisotonic with the physiological fluids, a fluid has to have anosmolarity of 300 mOsmol/L, but fluids with osmotic pressures rangingfrom 250 to 375 mOsmol/L are considered isotonic. Fluid with osmolarityless than 250 mOsmol/L are hypotonic whereas those with more than 375mOsmol/L osmolarity are hypertonic.

The pharmaceutically acceptable vehicle may comprise of bufferingagents. Examples of buffering agents that may be used in thepharmaceutical compositions of the present invention may be selectedfrom the group comprising boric acid or salts thereof, phosphoric acidor salts, thereof, citric acid or salts thereof, acetic acid or saltsthereof, tartaric acid or salts thereof, trometamol, and the like andmixtures thereof. A particularly preferred buffer of the presentinvention is the borate-boric acid buffer, which also acts to increasethe preservative efficacy of the preservatives added in the compositionof the invention. The term “borate-boric acid buffer” generally refersto any combination of boric acid and one or more of the conjugate basessuch that the pH is adjusted to the desired range, but preferably itrefers to a combination of boric acid and borax.

A pH adjusting agent may be used in order to adjust pH of thecompositions of the present invention in the range of about 5.5 to about7.5. Examples of pH adjusting agents include, but are not limited tohydrochloric acid, citric acid, phosphoric acid, acetic acid, sodiumhydroxide, potassium hydroxide, sodium carbonate, sodium hydrogencarbonate and the like, and mixtures thereof.

The pharmaceutically acceptable vehicle may comprise of viscosityenhancers. Viscosity enhancers may be added to the pharmaceuticalcomposition suitable for ophthalmic use to increase the viscosity of thecomposition and provide a longer residence time in the eye, providing alonger time for drug absorption and effect. The ophthalmic compositionsare usually packaged in sterile containers or bottles, which aregenerally made of plastics. Examples of such viscosity enhancers thatmay be used in the present invention includehydroxypropylmethylcellulose, hydroxypropylcellulose, polyvinyl alcohol,carboxyvinyl polymers, polyvinylpyrrolidone and the like, and mixturesthereof. In embodiments where the pharmaceutical composition is in theform of emulsion, the viscosity enhancers may be added after theemulsion process.

The pharmaceutical composition of the present invention may or may notcomprise of a co-solvent. It may be noted that the microemulsion isformed without the need of a co-solvent. In certain embodiments, aco-solvent may be used to enhance the surfactant effect. Examples of theco-solvents that may be used include but are not limited to propyleneglycol, polyethylene glycol, glycerine and the like and mixturesthereof. The co-solvent used is present in an amount of at least about1.2% w/v. The propylene glycol may be used in amounts ranging from about1.2% w/v to about 3% w/v, or preferably from about 1.5% w/v to about2.5% w/v, more preferably from about 1.5% w/v to about 2% w/v and mostpreferably in an amount of about 1.5% w/v.

The pharmaceutical composition of the present invention is sterile.Sterility is best achieved through sterile filtration using a sterilemembrane filter of 0.45 or 0.2 microns pore size and filtering into asterile container. Other methods of sterilization known in the art suchas dry heat, steam under pressure and gas sterilization can also be usedto make the pharmaceutical compositions for ophthalmic use sterile.Ophthalmic compositions are generally packaged in multiple usecontainers. Since there is a possibility of inadvertent bacterialcontamination of the formulation with repeated patient use, apreservative is generally added. Preservatives that do not cause patientsensitivity or that are compatible with the other ingredients in theformulation are generally used.

In one embodiment of the present invention, the pharmaceuticalcomposition comprises latanoprost, polyethylene glycol hydroxystearateand castor oil. The amount of the surfactant and the oil may be adjustedto get a submicron emulsion with an average droplet size less than 100nm and a percent transmission greater than 70%. In a preferredembodiment, the amount of castor oil varies from about 0.15% to about0.3% and the amount of polyethylene glycol hydroxystearate varies fromabout 0.25% to about 0.5% weight by volume of the composition. Thecomposition according to this embodiment is free of any quaternaryammonium compounds such as benzalkonium chloride which acts as apreservative. It was found that such composition was self emulsifying.It is always advantageous to have a self emulsifying system compared tothe conventional emulsions where an external energy supply is necessaryfor emulsification. It may be important to note that a proper selectionof oil, surfactant and optionally a co-solvent based on the solubilityof the drug, leads to an effective self emulsifying pharmaceuticalcomposition.

In one embodiment of the present invention, where an oil isincorporated, the composition was found to have a zeta potential in arange from about −0.1 mV to about −60 mV and the droplet size of the oildispersed in aqueous medium was not more than 100 nm. Preferredcompositions have zeta potential value of less than −20 mV. When suchcomposition was stored in natural low density polyethylene containers,the said composition was found to show no sorption problem when storedat room temperature.

According to one embodiment, the pharmaceutical composition is preparedby first dissolving the active ingredient completely in the oil bystirring. The emulsifier is melted and added to the oily phase and mixedproperly. Further, this phase is added drop wise under continuousstirring to an aqueous phase, comprising water for injection heated at55-60° C. This leads to the formation of an almost transparentmicro-emulsion or swollen micelles. To this propylene glycol is added atapproximately the same temperature. Further, the temperature is loweredto 25-30° C. and along with stirring the above emulsion phase is addedto a preformed solution of buffer, preservatives and other salts inwater for injection and having a pH of about 6.5-7.5. Finally, the pH isadjusted to 7.00 using HCl or NaOH; the volume made-up to 100% usingwater for injection and the composition is filtered aseptically using0.2 μm membrane filter.

In another embodiment, the pharmaceutical composition comprisesprostaglandin derivatives, stabilizing amount of polyethylene glycolhydroxystearate and pharmaceutically acceptable vehicle. Thepharmaceutical composition is prepared by first heating the polyethyleneglycol hydroxystearate (Solutol HS 15) in a separate glass beaker at65°-70° C. until it melts. To this, the drug and other ingredients i.epreservatives, buffers were added. The composition is diluted with waterfor injection and the pH was adjusted with sodium hydroxide andhydrochloric acid.

The pharmaceutical compositions of the present invention were tested forefficacy in reduction of intraocular pressure (IOP) in glaucomatousrabbits and normotensive dogs. It was observed that the compositions ofthe present invention significantly reduced the IOP in both glaucomatousrabbits and normotensive dogs as well as it had a significant effect(miosis) on the pupillary diameter.

According to one embodiment of the present invention the pharmaceuticalcomposition comprises oil along with polyethylene glycolhydroxystearate. In this embodiment, it was surprisingly found thatpharmaceutical compositions showed same therapeutic activity compared tothe composition that does not contain any oil, for example, Xalatan®.Without wishing to be bound by any theory, the applicants believe thatthis was surprising because generally the oil is known to hinder thediffusion of the drug and thereby affect the ocular availability.

The pharmaceutical compositions of the present invention were tested inNew Zealand White Rabbits, for ocular irritancy potential and systemictoxicity. The pharmaceutical composition of the present invention andpolyethylene glycol hydroxystearate (the excipient) both were tested.The test involved daily repeated ocular instillation for at least 14days. It was observed that on dosing of polyethylene glycolhydroxystearate (Solutol HS 15) at approximately 47 times the humanrecommended dose (HRD) and latanoprost present in the pharmaceuticalcomposition at approximately 48 times the HRD, no clinical sign orirritation in the eyes was observed. There were no statisticallysignificant alterations in body weight, % body weight gain, terminalbody weight, absolute and relative organ weights, differential cellcount of bone marrow, biochemical and hematological parameters afteradministration of polyethylene glycol hydroxystearate and latanoprost,as compared to the control group. Also the treatment with polyethyleneglycol hydroxystearate and latanoprost did not result into any gross ormicroscopical pathological lesion. Thus, it was found that thepharmaceutical composition of the present invention was safe and did notproduce any toxic reactions, ocular irritancy or systemic toxicity.

The following examples illustrate the scope of the present inventionwithout any limitation thereto.

EXAMPLE 1-2

The pharmaceutical composition of the present invention was prepared asdescribed in Table 1 below.

TABLE 1 Composition according to example 1 and example 2 Example 1Example 2 Ingredients Quantity % w/v Latanoprost 0.005 Propylene glycol1.5 Polyethyleneglycol 15 Hydroxy- 0.25 stearate (Solutol HS 15) Castoroil 0.15 Potassium sorbate 0.47 Borax 0.11 Boric acid 0.10 0.30 SodiumEdetate — 0.30 Sodium Hydroxide qs Hydrochloric acid qs Water forInjection (WFI) qsLatanoprost and castor oil was taken in a glass beaker and the mixturewas stirred continuously using a dry glass rod, untill completesolubilization of latanoprost takes place. Polyethyleneglycol 15Hydroxystearate (Solutol HS 15) was heated in a separate glass beaker at65°-70° C. until it melts. After melting, it was transferred to theabove oil phase and stirred using dry glass rod at 65-70° C. On completemixing, the oil phase solution temperature was allowed to come down to60° C. with gentle stirring. The temperature of the oil phase wasmaintained at around 55-60° C. This oil phase was added drop wise undercontinuous stirring to an aqueous phase comprising water for injectionheated at 55-60° C. This leads to the formation of transparentmicro-emulsion. This is followed by addition of propylene glycol at55-60° C. The temperature was allowed to come down to 25°-30° C. withgentle stirring, the stirring being continued for another 30-45 minutesat 25°-30° C. This was then added to a preformed solution of potassiumsorbate, borax and boric acid in water for injection and having a pH ofabout 6.5-7.5. Finally, the pH was checked and if required, was adjustedto 7.00 by adding HCl or NaOH solution. The volume was made up to 100%by rinsing the manufacturing vessels with WFI and the composition wasaseptically filtered through 0.2 μm membrane filter. The composition wasfilled into naturally occurring low density polyethylene containers.

The composition was stored at accelerated stability conditions i.e 25°C./60% RH or 40° C./75% RH. The stability studies results are given inTable 2.

TABLE 2 Accelerated stability studies of the composition of example 1stored in LDPE containers Latanoprost Assay (Limit: 90.0-110.0% Storageof Label Claim) Conditions Example 1 Example 2 Initial 109.11 103.59Fridge (2-8° C.) 1 Month 109.70 103.88 3 Month 107.67 102.48 6 month —101.00 25° C./60% RH 1 Month 108.11 103.16 3 Month 106.39 101.60 6 month— 99.71 40° C./75% RH 1 Month 106.94 100.77 3 Month 103.83 95.38 6 month— 93.50The results indicate that the pharmaceutical composition of the presentinvention is stable at room temperature, without any significantsorption of the drug to the LDPE containers. The data indicates that theassay of latanoprost remained unchanged upon storage at acceleratedcondition. This indicates that the micro-emulsion prepared according tothe present invention solved the sorption problem. The pharmaceuticalcomposition showed an average droplet size of about 100 nm; percenttransmittance was more than 80%, and zeta potential of −10 mV.

EXAMPLE 3-5

The pharmaceutical compositions of the present invention were preparedas described in Table 3 below.

TABLE 3 Example 3 Example 4 Example 5 Ingredients Quantity % w/vLatanoprost  0.005  0.005  0.005 Polyethylene Glycol — 1   1  Polyethyleneglycol 15 0.25 0.25 0.25 Hydroxystearate (Solutol HS 15)Castor oil 0.15 0.15 0.15 Potassium sorbate 0.47 — — Zinc chloride — 0.0025  0.0025 Borax 0.1  — — Boric acid 0.30 0.50 0.50 DisodiumEdetate 0.30 — 0.30 Tromethamine — q.s q.s Sodium Hydroxide qs — —Hydrochloric acid qs — — Water for Injection qs q.s q.s (WFI)Compositions according to Examples 3, 4 and 5 were prepared by processsimilar to the one described for Example 1 and 2. The droplet size, thezeta potential and percent transmittance values were comparable to thecomposition of Example 1 and 2.

EXAMPLE 6

The pharmaceutical composition of the present invention was prepared asdescribed in Table 4 below.

TABLE 4 Ingredients Quantity % w/v Latanoprost 0.005 Borax 0.11 Boricacid 0.10 Propylene glycol 1.5 Potassium sorbate 0.47 Polyethyleneglycol15 Hydroxystearate 0.25 (Solutol HS 15) Sodium hydroxide q.sHydrochloric acid q.s Water for injection (WFI) q.sSolutol HS 15 was taken in a glass beaker and heated at 65° to 70° C.until melted. After melting, it was transferred to the beaker containinglatanoprost & stirred till complete mixing. This phase was added towater for injection heated at 65°-70° C. drop wise with mild stirringfollowed by adding propylene glycol at 55°-60° C. under stirring. Inanother beaker potassium sorbate, disodium edetate, borax and boric acidwere dissolved in water for injection (WFI) under mild stirring. Thissolution was added to the above microemulsion phase at the temperatureof 20°-25° C. under stirring. The pH was adjusted to 7.00 by adding HClor NaOH solution. The volume was made up to 100% by rinsing themanufacturing vessel with WFI and filtered through 0.2 μm membranefilter. The composition thus prepared was stored in low densitypolyethylene containers and was subjected to accelerated stabilitystudy. The stability study results are tabulated in table 5.

TABLE 5 Accelerated stability studies of the composition of example 6stored in LDPE containers Latanoprost Assay (Limit: 90.0-110.0% ofStorage condition Label Claim) pH Initial 105.11 7.23 Fridge (2-8° C.) 1M (Up) 105.28 7.15 25° C./60% RH 1 M (Up) 103.43 7.09 1 M (Inverted)103.26 7.06 30° C./65% RH 1 M (Up) 102.02 6.68 1 M (Inverted) 102.356.99 40° C./75% RH 1 M (Up) 94.88 7.14 1 M (Inverted) 92.45 7.15It was observed that when the solution of example 6 was stored at roomtemperature or at 25° C./60% RH, there was no sorption problem observed.In view of the stability results, it may be advisable to store thesolution of example 6 at Fridge (2° C.-8° C.) or it may stored insuitable containers such as coated containers.

EXAMPLE 7

The pharmaceutical composition of the present invention containingbimatoprost as the prostaglandin is given in Table 6 below.

TABLE 6 Ingredients Quantity % w/v Bimatoprost 0.03 Propylene glycol 1.5Polyethyleneglycol 15 Hydroxystearate 0.3 (Solutol HS 15) Castor oil0.15 Potassium sorbate 0.47 Borax 0.11 Boric acid 0.3 Disodium EDTA 0.3Sodium Hydroxide qs Hydrochloric acid qs Water for Injection (WFI) qsThe composition of bimatoprost prepared according to this example wascharacterized by determining the average droplet size of the oilglobules, the percent transmittance and the zeta potential. The microemulsion showed an average droplet size of 67.6 nm; percenttransmittance of 90.2%, and zeta potential of −5.21 mV.

EXAMPLE 8 Comparative Example

TABLE 7 Ingredients Quantity % w/v Latanoprost 0.005 Borax 0.11 Boricacid 0.10 Propylene glycol 1.5 Potassium sorbate 0.47 Sodium hydroxideq.s Hydrochloric acid q.s Water for injection (WFI) q.sThe above composition was prepared by simple mixing of the mentionedingredients. When the composition was stored in LDPE containers, therewas unacceptable reduction in the latanoprost assay (see table 8 below)indicating an unacceptable sorption of latanoprost to the containers.

TABLE 8 Accelerated stability studies of the composition of example 8stored in LDPE containers Latanoprost Assay (Limit: 90.0-110.0% ofStorage condition Label Claim) pH Initial 97.82 7.15 Fridge (2-8° C.) 1M 91.50 7.24 2 M 88.55 7.20 3 M 79.38 7.24 25° C./60% RH 1 M (Up) 85.747.11 1 M (Inverted) 85.68 7.01 2 M (Up) 79.38 7.11

EXAMPLE 9 Comparative Example

TABLE 9 composition of comparative example Quantity Ingredients % w/vLatanoprost 0.005 Propylene glycol 1.5 Polysorbate 80 0.25 Castor oil0.15 Potassium sorbate 0.47 Borax 0.11 Boric acid 0.3 Disodium Edetate0.3 Sodium Hydroxide qs Hydrochloric acid qs Water for Injection (WFI)qsThe composition prepared according to this example showed an averagedroplet size of 173 nm; percent transmittance 35.0%, and zeta potentialof −8.36 mV.

We claim:
 1. A pharmaceutical composition suitable for ophthalmic usecomprising 0.005% w/v latanoprost or a pharmaceutically acceptable salttherof, 0.15% w/v castor oil, 0.2 to 0.75% w/v of polyethylene glycolhydroxystearate, a co-solvent, a chelating agent, a preservative, andpharmaceutically acceptable vehicle, wherein the ratio of oil topolyethylene glycol hydroxystearate is less than 1.0, wherein thecomposition is in the form of a self-emulsifying micro-emulsion withaverage droplet size of about 100 nm or less and a zeta potentialbetween −0.1 mV to −20 mV, wherein the composition does not comprise acationic surfactant, and wherein the composition does not comprise aquaternary ammonium compound.
 2. The pharmaceutical composition asclaimed in claim 1 Wherein the emulsion has an average droplet size ofless than 100 nanometers in diameter.
 3. The pharmaceutical compositionas claimed in claim 2, wherein the emulsion has a percent transmissiongreater than 70%.
 4. The pharmaceutical composition as claimed in claim2, wherein the emulsion has a percent transmission greater than 80%. 5.The pharmaceutical composition as claimed in claim 1 wherein thecomposition does not show any clinical sign of ocular irritation whentested in rabbits.